Feasibility study : use of cine-MRI in MR-guided particle therapy

Abstract

Cinematic Magnetic Resonance Imaging (cine-MRI) are fast time-resolved 2D MRI sequences that allow online visualization of organ motion without exposing patients to ionizing radiation. In this study, the potential of cine-MRI for the definition of animage-based gating criterion in particle therapy of pancreatic cancer is investigated. Transversal cine-MRI are employed to segment the pancreas, since they can provide information on tissue changes in the beam-path during delivery. Volunteer data were acquired on 10 different acquisition days. An image-based gating window was defined based on the breathing-curve (BC) of the first day (end-exhale breathing phase ±30%). The superposition of the pancreas segmentations in this window was calculated. For other days of data acquisition, the agreement with this initial superposition contour was evaluated by using different segmentation image similarity metrics. Additionally, a motion analysis of the pancreas was performed. From the metrics comparisons, a gating criterion was defined to establish when irradiation can be allowed. An evaluation of the dosimetric differences due to differences in the segmentations achieving the criterion and the spatial location of the organs was carried out for a proton treatment. Although the method applied was subjected to several limitations, it was proved to be feasible.